I understand that phi. mercury is a prepared substance but it appears that the starting mineral matter exhibits the same layered crystaline structure. I think Fulcanelli in the quotes you posted about catching a fish in the net corresponds to this operation:

Yes, correct, one of the starting matters; because there's more than just one (don't fall for the "one matter only" ruse, it's a "philosophical" booby-trap designed to frustrate inexperienced seekers by making them waste their time and money in a hopeless quest to literally find one, single, naturally-occurring matter that will perform all of what they read the alchemists describe in their books, without need of anything else, which, of course they will never, ever, not even in a million years, be able to find anywhere in nature since nature can't make such a "matter"; it is the alchemist himself who does this by putting together the right matters, in the right proportions, and making them react in the right manner.)